SPring-8, the large synchrotron radiation facility

Scientists of Toyohashi University of Technology (Yoshiyuki Sakaki, President) and Ahresty Corporation (Arata Takahashi, President) in cooperation with those of Japan Synchrotron Radiation Research Institute (JASRI; Tetsuhisa Shirakawa, President) clarified, for the first time in the world, the relationship between the arrangement pattern of micropores, a cause of metal fatigue, produced on the surface of aluminum alloys in a die-casting process　and fatigue crack initiation, using the high-brilliance X-rays of SPring-8.

The die-casting process,^*1 a metal mold casting in which molten metal is pressed in a mold, has been applied to manufacturing thin-profile parts used for automobiles, home appliances, construction, and industrial machineries, because the process enables the manufacturing of parts with high dimensional accuracy and yield. Recently, the die-casting process has been advanced; a new method to produce parts requiring high reliability, such as wheels and related parts, has been developed and is already in practical use. However, the results of the fatigue test using parts manufactured by this method revealed that the timing and location of fatigue crack initiation differ each time. Therefore, such parts cannot be used in aircraft, which require very high reliability. Although the relationship between micropores and metal fatigue has been pointed out, methods for analyzing and observing the relationship have not been available, leading to the inability to examine it. This time, the high-brilliance X-rays of SPring-8 have enabled this analysis.

The research group statistically analyzed the relationship between the high-density micropores in the surface layer and the fatigue characteristics of a metal material by CT scan using the high-brilliance X-rays of SPring-8, and clarified the relationship between the arrangement pattern of micropores and fatigue crack initiation. The results indicate that the application of the die-casting process to automobile and aircraft parts, which has been difficult conventionally, will become possible by further improving the reliability and performance of the process.

The achievements of this research were obtained by a joint research group that includes Hiroyuki Toda, a professor of Toyohashi University of Technology; Shunzo Aoyama, a chief scientist, Masato Onodera, a section chief, and Ryosuke Furusawa, a section staff member, of the Technical Division of Ahresty Corporation; Kentaro Uesugi, a research scientist, Akihisa Takeuchi, an associate senior scientist, and Yoshio Suzuki, an associate chief scientist, of JASRI. The achievement was published online in the scientific journal Acta Materialia on 2 June 2011.

Publication:
"Statistical assessment of fatigue crack initiation from sub-surface hydrogen micropores in high-quality die-cast aluminum Original Research Article"
Hiroyuki Toda, Shotaro Masuda, Rafael Batres, Masakazu Kobayashi, Shunzo Aoyama, Masato Onodera, Ryosuke Furusawa, Kentaro Uesugi, Akihisa Takeuchi and Yoshio Suzuki
Acta Materialia 59(12), 4990-4998 (2011), published online 26 May 2011